The present invention relates to a digital signal recording/reproducing apparatus of the rotary head type and more particularly to a digital signal recording/reproducing apparatus suitable for variable-speed recording/reproduction.
As an apparatus using a rotary head formed of a cylinder with magnetic heads mounted thereon for recording/reproducing a digital signal on a magnetic tape, there is a PCM recorder, for example, as disclosed in U.S. Pat. No. 4,227,221. By such a system using a rotary head, improvement in signal recording density is achieved and also a reproducing signal with high quality can be obtained.
The present applicant has already made a number of patent applications for the inventions relative to the PCM recorder and been granted U.S. Pat. Nos. 4,309,726, 4,617,599, 4,677,622, 4,649,542, 4,594,621, 4,646,301, 4,704,640, 4,646,170, 4,660,200, etc.
Functions of such a PCM recorder include long-time recording/reproduction performed by its operation at 1/N-times normal speed and high-speed dubbing performed by its recording/reproduction of a signal at N-times normal speed. These functions are produced by an arrangement so that the number of revolutions of the cylinder, i.e., that of the rotary head, and the feed speed of the tape are simultaneously changed so that recording/reproducing at, for example, half speed (1/N-times normal speed where N=2) or double speed (N-times normal speed where N=2) are performed.
In the above mentioned prior art, the number of revolutions of the cylinder, i.e., of the rotary head, is changed in the reproduction mode at N-times normal speed or 1/N-times normal speed, and as a result, the frequency of the signal reproduced by the rotary head is subjected to variation. Hence, there was such a problem that the signal frequency was lowered in the mode at low-speed (for example, at 1/2-times normal speed=half speed), and therefore, the head sensitivity was lowered and the S/N ratio deteriorated. Further, because the reproducing frequency from the rotary head was varied depending upon the modes of operation, there also was such a problem that it was required to switch analog circuits such as equalizers, frequencies of a VCO of a data strobing circuit, or the like in order to achieve correct demodulation of the signal.